Inflammation is a response of vascularized tissues to infection or injury and is affected by adhesion of leukocytes to the endothelial cells of blood vessels and their infiltration into the surrounding tissues. In normal inflammation, the infiltrating leukocytes release toxic mediators to kill invading organisms, phagocytize debris and dead cells, and play a role in tissue repair and the immune response. However, in pathological inflammation, infiltrating leukocytes are over-responsive and can cause serious or fatal damage. See, e.g., Hickey, Psychoneuroimmunology II (Academic Press 1990).
The integrins are a family of cell-surface glycoproteins involved in cell-adhesion, immune cell migration and activation. Alpha-4 integrin is expressed by all circulating leukocytes except neutrophils, and forms heterodimeric receptors in conjunction with either the beta1 or beta7 integrin subunits; both alpha-4 beta-1 (α4β1) and alpha-4 beta-7 (α4β7) dimers play a role in the migration of leukocytes across the vascular endothelium (Springer et al., 1994 Cell 76: 301-14; and Butcher et al., 1996 Science 272: 60-6) and contribute to cell activation and survival within the parenchyma (Damle et al., 1993 J. Immunol. 151: 2368-79; Koopman et al., 1994 J. Immunol. 152: 3760-7; and Leussink et al., 2002 Acta Neuropathol. 103:131-136).
Specifically, alpha-4 beta-1 (also known as very late antigen-4 (VLA-4)), binds to vascular cell adhesion molecule-1 (VCAM-1)(Lobb et al., 1994 J. Clin. Invest. 94:1722-8), which is expressed by the vascular endothelium at many sites of chronic inflammation (Bevilacqua et al., 1993 Annu. Rev. Immunol. 11: 767-804; and Postigo et al., 1993 Res. Immunol. 144:723-35). The alpha-4 beta-7 dimer interacts with mucosal addressin cell adhesion molecule (MAdCAM-1), and mediates homing of lymphocytes to the gut (Farstad et al., 1997 Am. J. Pathol. 150: 187-99; and Issekutz et al., 1991 J. Immunol. 147: 4178-84). Expression of MAdCAM-1 on the vascular endothelium is also increased at sites of inflammation in the intestinal tract of patients with inflammatory bowel disease (IBD) (Briskin et al., 1997 Am. J. Pathol. 151: 97-110).
Adhesion molecules such as alpha-4 integrins are potential targets for therapeutic agents. For instance, the VLA-4 receptor, of which alpha-4 integrin is a subunit, is an important target because of its interaction with a ligand residing on brain endothelial cells. Diseases and conditions resulting from brain inflammation have particularly severe consequences. In another example, the alpha-4 beta-7 integrin dimer is an important target due to its involvement in lymphocyte homing and pathological inflammation in the gastrointestinal tract.
Alpha-4 beta-1 integrin is expressed on the extracellular surface of activated lymphocytes and monocytes, which have been implicated in the pathogenesis of acute inflammatory brain lesions and blood brain barrier (BBB) breakdown associated with multiple sclerosis (MS) (Coles et al., 1999 Ann. Neurol. 46(3): 296-304). Agents against alpha-4 integrin have been tested for their anti-inflammatory potential both in vitro and in vivo in animal models. See Yednock et al., 1992 Nature 356: 63-66; U.S. Pat. No. 5,840,299 issued to Bendig, et al. on Nov. 24, 1998, and U.S. Pat. No. 6,001,809 issued to Thorsett et al. on Dec. 14, 1999. The in vitro experiments demonstrate that alpha-4 integrin antibodies block attachment of lymphocytes to brain endothelial cells. Experiments testing the effect of alpha-4 integrin antibodies on animals having an artificially induced condition simulating multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), have demonstrated that administration of anti-alpha-4 integrin antibodies prevents inflammation of the brain and subsequent paralysis in the animals. Collectively, these experiments identify anti-alpha-4 integrin antibodies as potentially useful therapeutic agents for treating multiple sclerosis and other inflammatory diseases and disorders.
In another specific example of pathological inflammation involving alpha-4 integrins, Crohn's disease (CD) is a chronic, incurable, relapsing, transmural inflammation of the intestinal tract. The disease is characterized by inappropriate immune cell migration and activation in the intestinal mucosa involving T cells, macrophages and neutrophils (Schreiber et al., 1991 Gastroenterology 101: 1020-30). First-line medical therapies for Crohn's disease include 5-aminosalicylates (5-ASAs), which have low efficacy, and corticosteroids, which have various short- and long-term side effects (Munkholm et al., 1994 Gut 35: 360-2). Patients refractory to first-line therapies are treated with immunosuppressive agents such as azathioprine, 6-mercaptopurine, and methotrexate, but these agents have a slow onset of action and potentially serious side effects (Stein et al., 2001 Surg. Clin. North Am. 81: 71-101, viii). More recently, biologic agents with a faster onset of action have been introduced for use in treating Crohn's disease, but such agents are similarly plagued by issues such as long-term efficacy and side effects.